This invention relates to an apparatus and method for preparing a coated optical fiber for coupling at a free end to an optical face.
A conventional optical fiber comprises a core, a cladding and a protective coating. The coating that is conventionally used on optical fiber is a UV curable polymer material. The mechanical nature of the coating depends on the conditions to which it has been exposed, particularly the extent to which is has been exposed to UV radiation.
In making measurements on a optical fiber, it may be necessary to couple an end face of the fiber under test (the “test fiber”) to an optical fiber test or measurement instrument, such as an optical fiber time domain reflectometer (OTDR), through a buffer fiber. In order to provide a satisfactory optical coupling between the test fiber and the buffer fiber, an end segment of the test fiber may be brought into axial alignment with an end segment of the buffer fiber using a fiber aligner. A suitable fiber aligner is described in U.S. Pat. No. 5,949,938.
The aligner that is described in U.S. Pat. No. 5,949,938 is specifically designed for aligning a single mode test fiber with a similar single mode buffer fiber. Because single mode fiber cores are very thin, a single mode fiber must be aligned with a high degree of precision. Because the coating of the fiber may not have a precise geometrical relationship with the core, it is necessary to strip the coating from the end segment of the test fiber before placing it in the aligner, which then uses the cladding surfaces to align the cores. It is possible to strip some coatings using chemical solvents, but in an industrial setting, the use of these solvents is not desirable when considering issues relating to environment and safety. When the coating of a conventional optical fiber is mechanically stripped, the coating material does not usually remain in the form of a sleeve or tube that slides off the end of the fiber but, on the contrary, the coating breaks up into discrete conglomerates and particles. These particles and other debris must be removed from the end segment of the fiber since they could interfere with proper positioning of the end segment of the fiber in the aligner.
U.S. Pat. No. 5,949,938 discloses a technique in which an operator manually strips an end segment of the test fiber, fits the test fiber in a fiber clip and then manually cleaves the test fiber. The operator then manually advances the test fiber so that the cleaved end face is positioned in the aligner in contact, and in alignment, with the buffer fiber. This technique is well suited for low volume work because it does not require expensive fiber handling equipment, but its reliance on operator time and skill limits its efficiency and makes it less than optimum for high volume use.
The conventional mechanical technique for stripping an optical fiber involves placing the end segment of the fiber in a stripper, closing the stripping blades about the fiber close to the end face of the fiber, and then drawing the end segment of the fiber through the stripping blades, so that the stripping blades pass along the fiber in the direction towards the end face of the fiber.
When the coating is stripped from an optical fiber, a high electrostatic charge is generated on the exposed surface of the fiber cladding. The electrostatic charge may attract particles of coating material, dust and debris. These particles must be removed before the fiber is placed in the fiber aligner, since otherwise they could interfere with alignment of the fiber. In principle, it would be possible to remove particles from the surface of the cladding by wiping, but wiping itself tends to create an electrostatic charge and so even though the wiping may be effective to remove larger particles of cladding material, dust particles in the ambient air may be attracted to the exposed surface of the cladding.
It is known to use an electric arc to clean the cladding of an optical fiber. The electric arc vaporizes small particles (smaller than about 50 μm) adhering to the cladding so that the cladding and the end face of the fiber are in pristine condition.